Abstract:
To test whether aspartame-induced antinociception involves opioidergic mechanisms, male IRC mice received either distilled water or aspartame solution (0.16% w/v) and then subcutaneously injected with either saline or naloxone, an opioid receptor antagonist. Aspartame solution and distilled water were given for one day or 14 days. Latency responses, measured via the hot plate and the tail flick methods, were normalized into an index of analgesia. Within-subject interaction effects were significant for the variables of aspartame treatment, behavioral test applied, duration of administration, and presence of naloxone. The mean index of analgesia of aspartame-treated mice was higher by 93% compared to that of the untreated controls following a long-term (14-day) duration of administration. In addition, the presence of naloxone was observed to inhibit aspartame-induced antinociception during the said period. On the other hand, following short-term (24-hour) duration of administration, the mean index of analgesia of water- treated mice given with naloxone was higher by 135% compared to those of the untreated controls. The findings suggest that opioidergic mechanisms and both the spinal and supraspinal structures may be involved in aspartame-induced antinociception which could be influenced by the duration of aspartame treatment. However, the results do not negate the possible transient antinociceptive effect of naloxone in the absence of aspartame.
